The exact etiology of dental caries is not known with precision. Probably it results from a multiplicity of factors. It is well established, however, that caries is intimately involved with dental plaque and calculus, and that fluorides play an active role in the prevention of caries, rendering tooth enamel less susceptible to solubilization by the low pH of the plaque milieu.
Currently, fluorides are employed for tooth care as soluble inorganic fluorides to be taken internally such as in drinking water; as relatively insoluble fluoride salts, such as stannous fluoride in toothpaste formulations; or as applied directly to the teeth by a dentist. In recent years, it was found that certain organic amine hydrofluoride acid addition salts are effective in the prevention of dental caries, like the inorganic fluorides. The fluorides, however, as currently used have little or no effect on the formation of dental plaque.
Historically, the diphenyliodonium salts and substituted diphenyliodonium salts have been used as germicides and antiseptics. More recently, the thienyliodonium salts such as, for example, 4-chlorophenyl-2-thienyliodonium chloride, have been found to be much more effective as antimicrobials, since they have a broader spectrum of antimicrobial activity against both gram-positive and gram-negative and are more effective against microbes at lower concentrations; see, for example, U.S. Pat. No. 3,763,187, patented Oct. 2, 1973.
In research evaluating the application of antimicrobials for the control of specific microorganisms in the oral cavity implicated in the etiology of dental caries and periodontal disease, the unexpected discovery was made by us that antimicrobial activity can be separated from antiplaque activity. The dental literature has established and accepted the concept that plaque formation is a common factor in both dental caries and periodontal disease. It is taught in the dental literature that the organisms responsible for plaque formation reside primarily on tooth surfaces. The mechanism for their adherence to the tooth surface depends upon the synthesis of complex polysaccharides which, when synthesized in sufficient amounts, form the basis for plaque. Our unexpected observation is that certain thienyliodonium salts which also have antimicrobial activity at high concentrations and long exposure times have the ability at low concentrations and short exposure times to inhibit the formation of plaque without killing the organisms which cause plaque to be formed. Our research teaches that the ultimate removal of the specific organisms involved in plaque formation comes about not through the antimicrobial activity of the said compounds but through the prevention of plaque formation and the subsequent removal of the specific organisms by the abrasion due to the eating and ordinary oral hygiene such as brushing. Effective prevention of plaque formation requires consistent periodic utilization of the thienyliodonium salt, advantageously after meals, for a sufficient period of time. The following information supports this:
1. The basic activity of interest is the ability of the thienyliodonium salt to inhibit the formation of dental plaque but not to interfere with the viability of the organisms in question when treated with the level of the said salt for a short time period in the order of minutes. Studies show that time is a critical factor when considering this activity. Short contact periods apparently do not adversely affect the growth of Streptococcus mutans, the most important organism involved in plaque formation, but we know from our studies that intermittent daily usage in vivo is sufficient to inhibit the formation of plaque.
2. The mechanism by which plaque formation is inhibited has not been elucidated at this time. Sucrose from the environment of the plaque-forming organisms is converted through a series of metabolic and enzymatic steps into extracellular polysaccharides. These polysaccharides are the backbone of the plaque matrix. Inhibition, therefore, could occur at any point along this path.
3. The use of the thienyliodonium salts should not be presumed to take any particular form. Rather, any formulation that maintains the stability and activity characteristics of these salts is useful.
Both chlorhexidine and cetylpyridinium chloride (the latter available commercially as Micrin Plus mouthwash) have been used as anti-plaque agents; J. Periodont. Res. 8, 57-62, (1973) and J. Periodont. 40, 299, (1969).